docs: def write_cyc(fn, this, conv=1.0):
      """ Write the lattice information to a cyc.dat file (i.e., tblmd input file)
      """
  
      lattice = this.get_cell()
  
      f = paropen(fn, "w")
      f.write("<------- Simulation box definition\n")
      f.write("<------- Barostat (on = 1, off = 0)\n")
      f.write("  0\n")
      f.write("<------- Box vectors (start)\n")
      f.write("  %20.10f %20.10f %20.10f\n" % (lattice[0][0]*conv, lattice[1][0]*conv, lattice[2][0]*conv))
      f.write("  %20.10f %20.10f %20.10f\n" % (lattice[0][1]*conv, lattice[1][1]*conv, lattice[2][1]*conv))
      f.write("  %20.10f %20.10f %20.10f\n" % (lattice[0][2]*conv, lattice[1][2]*conv, lattice[2][2]*conv))
      f.write("<------- Box vectors (end)\n")
      f.write("  %20.10f %20.10f %20.10f\n" % (lattice[0][0]*conv, lattice[1][0]*conv, lattice[2][0]*conv))
      f.write("  %20.10f %20.10f %20.10f\n" % (lattice[0][1]*conv, lattice[1][1]*conv, lattice[2][1]*conv))
      f.write("  %20.10f %20.10f %20.10f\n" % (lattice[0][2]*conv, lattice[1][2]*conv, lattice[2][2]*conv))
      f.write("<------- Mass and gamma of the box (used in connection with the barostat)\n")
      f.write("  240 0.005\n")
      f.write("<------- Stress tensor (start)\n")
      f.write("  0 0 0\n")
      f.write("  0 0 0\n")
      f.write("  0 0 0\n")
      f.write("<------- Stress tensor (end)\n")
      f.write("  0 0 0\n")
      f.write("  0 0 0\n")
      f.write("  0 0 0\n")
      f.close()